Microstability of β ~ 1 tokamak equilibria
Microstability of β ~ 1 tokamak equilibria
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Date
2023-03-01
Authors
Gaur, Rahul
Abel, Ian G.
Dickinson, David
Dorland, William D.
Advisor
Citation
Gaur, R., Abel, I., Dickinson, D., & Dorland, W. (2023). Microstability of β ~ 1 tokamak equilibria. Journal of Plasma Physics, 89(1), 905890112.
Abstract
High-power-density tokamaks offer a potential solution to design cost-effective fusion devices. One way to achieve high power density is to operate at a high β
value (the ratio of thermal to magnetic pressure), i.e. β∼1. However, a β∼1
state may be unstable to various pressure- and current-driven instabilities or have unfavourable microstability properties. To explore these possibilities, we generate β∼1
equilibria and investigate their stability. First, we demonstrate the generation of high- β
equilibria with the computer code VMEC. We then analyse these equilibria to determine their stability against the infinite- n
ideal-ballooning mode. We follow that by engaging in a detailed microstability study using the GS2 code, beginning with assessments of electrostatic ion-temperature-gradient and trapped election mode instabilities. We observe interesting behaviour for the high- β
equilibria – stabilization of these modes through two distinct mechanisms – large negative local shear and reversal of electron precession drift. Finally, we perform electromagnetic gyrokinetic simulations and observe enhanced stability in the outer core of high- β
equilibria and absence of kinetic ballooning modes in the negative-triangularity, high- β
equilibria. The enhanced outer-core stability of high- β
equilibria is different from their lower- β
counterparts and offers an alternative, potentially favourable regime of tokamak operation.